The invention relates to a measuring chamber, preferably a flow-through chamber comprising a bottom part and a top part which are at least partially transparent to the excitation and measuring radiation and together form a measuring channel, with luminescence-optical sensor elements provided in a sensing area.
Such measuring chambers are used for simultaneously measuring several parameters in liquid or gaseous samples which are introduced into the measuring chamber, or, in the instance of flow-through chambers, delivered by means of suitable pumping or suction devices. In M. J. P. LEINER, Sensors and Actuators B29 (1995) 169-173, for example, a measuring chamber for simultaneously determining pH, PCO2 and PO2 in blood is described under the title of xe2x80x9cOptical sensors for in vitro blood gas analysisxe2x80x9d, the measuring chamber being configured as a flow-through cell. This cell essentially consists of two injection-molded parts made of plastic material that is transparent to the excitation and measuring radiation emitted by the luminescence-optical sensors used. Fittings for connection of sample inlet and outlet are integrated at the two ends of the measuring cell. The bottom part of the cell has three cylindrical cavities for the sensor elements in a sensing area. The top part of the measuring cell contains a groove-shaped cavity which together with the bottom part forms the measuring channel with a sample volume of about 40 xcexcl. Two-armed light guides directed towards the bottom part of the measuring chamber are provided for excitation of the luminescence indicator in the individal luminescence-optical sensor elements and for detection of the luminescence radiation.
A halogen light source constitutes the excitation source, the required wavelengths being obtained with the use of suitable filters. The luminescence radiation emitted by the individual sensor elements is transmitted via separate light guides and cut-off filters to detectors which are connected to the evaluation unit. The measuring chamber is configured as a disposable measuring cell and is inserted for measurement into a temperature-controlled measuring device at a constant temperature of 37xc2x0 The sensor elements, which have the shape of small disks and are built in layers, consist of an adhesive layer, a transparent carrier layer, a sensing layer and an optical cover layer, as seen in the direction of the measuring channel. The optical cover layer or isolation layer serves to protect the indicator layer of the sensor against stray light from the sample or the environment (such as natural fluorescence or ambient light), thus optically decoupling the sensor elements. After the individual sensor elements have been inserted into the cylindrical cavities in the bottom part, the two parts of the measuring chamber are glued together. Due to the different kinds of materials encountered by the sample in the measuring channel, troubles may arise upon filling the measuring channel, since different materials, such as the wall of the measuring cell and the optical cover layer, will not be uniformly wetted by the sample, which may lead to air bubbles or non-homogeneous flow conditions. As a consequence, the sample may flow around the sides of the sensor element.
Another disposable measuring element for simultaneously measuring a plurality of different sample components is described in EP 0 354 895 B1, which comprises a sensor part and a sampling part connected thereto. The sensor part is provided with a Continuous sample channel containing several sensor elements. Excitation of the sensor elements and detection of the measuring radiation takes place via light guides which are guided to the transparent sensor part from outside.
It is the object of the present invention to propose a measuring chamber on the basis of the above state of the art, which should be simple and inexpensive to produce, featuring homogeneous flow conditions in the measuring channel and permitting a greater number of individual parameters to be determined while using essentially the same sample volume as before.
According to the invention this object is achieved by providing a longitudinal groove each in the bottom part and in the top part, which grooves together form the measuring channel, and by arranging for sensor elements to be placed in the longitudinal grooves of the bottom part and the top part, each of which elements is coated with an optical cover layer covering the entire sensing area. These provisions of the invention will allow the number of luminescence-optical sensor elements to be doubled while the sample volume will essentially remain the same, as the sensor elements will be positioned in the bottom part as well as in the top part. Since the longitudinal groove is provided with a continuous optical cover layer covering the entire sensing area in the bottom part as well as in the top part, the two cover layers will form a shallow sample channel or capillary gap, in which the sample will be able to pass through the measuring channel without developing air bubbles or forming undesirable flow profiles.
It will be of special advantage to extend the optical cover layer in the bottom and top parts up to the two edges of the longitudinal groove, thus forming a homogeneous lining of the measuring channel.
According to a preferred variant a plurality of sensor elements could be assembled to form a group. Groups of one and the same kind of sensor elements may be employed to obtain a mean value from a number of individual measurements, for instance.
The individual sensor elements may be positioned in cavities at the bottom of the longitudinal groove and covered by a continuous optical cover layer.
In a further variant of the invention the proposal is put forward that the optical cover layer extend into the areas between adjacent sensor elements to optically decouple adjacent sensor elements in these areas.
According to another variant offering special advantages, the bottom part and the top part of the measuring chamber are configured as essentially symmetrical parts, and are provided with inner surfaces facing each other and containing the longitudinal groove holding the sensor elements, and outer surfaces parallel to the inner surfaces, and lateral surfaces essentially normal to the outer surfaces. As opposed to state-of-the-art measuring chambers manufacturing, will be considerably facilitated if the bottom and top parts of the measuring chamber are injection-molded parts of identical design which can be provided with different sensor elements or groups of sensor elements. This design will permit the use of sensor elements for pH, PCO2 and PO2 measurement in the bottom part, and combining of the bottom part with a top part carrying sensor elements for determining different electrolytes, such as sodium, potassium and calcium. On the other hands the bottom part measuring the blood gas parameters pH, PO2 and PCO2, can be combined with a top part carrying biosensors for determining lactate, glucose, urea, creatinine, etc. The advantage is that individual parts of the measuring chamber may be provided with a group of sensor elements, and that such parts can be assembled on account of their symmetry to form different types of measuring chambers, depending on the parameters desired.
According to the invention such symmetrical parts of a measuring chamber, essentially in the shape of a parallel epiped, will permit optical excitation of the individual sensor elements via the lateral faces, and detection of the measuring radiation via the outer faces of the symmetrical parts. In this way the excitation light is optically decoupled from the measuring light at an early stage, i.e., in the respective part of the measuring chamber. The general principle of optical separation of excitation radiation and measuring radiation in a transparent carrier element is described in AT 383 684 B. That description proposes a carrier element with parallel boundary faces (comparable to the bottom and top part of this invention), which is provided with a sensor layer on one of these faces, the sensor layer being subject to excitation light from a radiation source. The light from the radiation source is incident on the sensor layer through an aperture, the measuring radiation generated in this way being directed essentially normally to the direction of the excitation radiation, towards a detector positioned at a face on the lateral wall of the carrier element. Light guidance in the carrier element is essentially due to total reflection of the measuring radiation at the boundary faces of the carrier element. This principle is reversible, i.e, excitation may take place via the lateral surface and detection via the surface parallel to the sensor face.
It is of special advantage to arrange the sensor elements of the bottom part and the top part in opposing pairs. In this way a laterally placed light source may be used to subject two sensor elements each to excitation radiation, whose measuring radiation is detected via the outer face of the bottom part and the outer face of the top part. The measuring radiation of the two sensor elements is optically decoupled via the two optical cover layers lining the measuring channel.
In order to prevent mutual optical influences between the sensor elements positioned side by side in the bottom or top part, they may be individually contacted with optical waveguides. Another possibility would be to take optical or electronic measures as described in EP 0 793 090 A1.
To improve the coupling-in of excitation light into the bottom and/or top part of the measuring chamber it is proposed for each sensor element to provide at least one lateral surface of a measuring chamber part with an optical element, preferably a collimating lens, a Fresnel lens or a grating, which will couple in or focus the excitation radiation in the direction of the sensor elements.
The measuring chamber according to the invention can be thermostatted in a simple way, by providing a heatable foil between the bottom part and the top part, which should extend into the measuring channel. Contrary to state-of-the-art designs it will not be necessary to overcome the heat-insulating effect of the wall of the measuring chamber for thermostatting the sample, since all sensor elements are temperature-controlled in the same way directly inside the measuring channel by utilizing the good thermal conductivity of the aqueous sample.
Preferably, the heatable foil may be provided with an electrically conductive layer in the shape of a meandering strip conductor.
In further development of the invention a separating foil may be provided between the bottom part and the top part, which will divide the measuring channel into two separate partial channels. This will permit the measuring of a calibrating medium or quality control means in one partial channel of the measuring chamber, while the sample components are being detected in the other partial channel at the same time. In this application one and the same kind of sensor elements are preferably arranged in opposing pairs and subjected to excitation radiation from the same light source.
It will further be possible to use the separating foil simultaneously as heating foil for temperature control of the measuring chamber.